This application claims priority and contains subject matter related to Japanese Patent Application No. 11-371936 filed in the Japanese Patent Office on Dec. 27, 1999 and the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an apparatus wherein a DC (direct current) motor is used to provide the driving force for performing mechanical operations, and wherein stabilization of the rotational speed of the DC motor and control of cumulative rotation numbers of the DC motor are required. More particularly, the present invention relates to a rotation detecting apparatus and a rotation control apparatus for the DC motor wherein rotational operations of the rotor of the DC motor are controlled by detecting at least one of the rotational direction, the rotational speed, the cumulative rotation number, and the rotational position of the rotor.
2. Discussion of the Background
A brush-using DC motor is often used to provide the driving force for mechanical operations in a camera, for example: in zooming operations, wherein photographic lenses including a zoom lens are zoomed; in focusing operations, wherein at least one of a photographic lens and an imaging device is moved along an optic axis of the photographic lens for focusing based on the distance from an object to an image focusing point; and in film feeding operations, wherein a photographic film is wound and rewound.
In the brush-using DC motor, plural fixed magnetic poles are formed in a stator by employing a permanent magnet, etc. A DC drive current is switched corresponding to the rotational angle of the rotor, and is applied to plural rotor coils forming plural magnetic poles of the rotor through a commutator which rotates together with the rotor and through a brush which is in sliding contact with the commutator. Thereby, the rotor rotates.
There are, for example, five types of apparatuses using a motor as a driving force: (1) the type where uni-directional rotations of the motor are used, and the rotational speed of the motor is required to be kept constant; (2) the type where uni-directional rotations of the motor are used, and cumulative rotation numbers of the motor, that is, the total driving amount of the motor, are required to be controlled; (3) the type where bi-directional rotations of the motor (i.e., a forward rotation and a reverse rotation) are used, and the rotational speed only on uni-directional rotations of the motor is required to be kept constant; (4) the type where bi-directional rotations of the motor are used, and each rotational speed on bi-directional rotations of the motor is required to be kept constant; and (5) the type where bi-directional rotations of the motor are used, and cumulative rotation numbers on uni-directional rotations of the motor are required to be controlled.
With regard to the rotation control method of the motor in an apparatus, there are, for example, two types of apparatuses according to their uses and operation environmental conditions: (1) the type where the rotational speed of the motor is controlled by changing a drive voltage for driving the motor; and (2) the type where the rotational speed of the motor is controlled by a chopping control wherein a drive voltage is intermittently applied to the motor.
As an example of the above-described brush-using DC motor, FIG. 30 illustrates a three-pole motor. In the three-pole motor, electricity is fed to a commutator CM0 which is in sliding contact with a pair of electrode brushes B01 and B02 from a DC drive power supply E0 through the paired electrode brushes B01 and B02. The paired electrode brushes B01 and B02 are brought into contact with the commutator CM0 on rotational angle positions different by 180xc2x0. The commutator CM0 includes three pieces which form a cylindrical surface and rotates together with a rotor of the DC motor. The three pieces of the commutator CM0 are separated at equally angled interval of about 120xc2x0. Three rotor coils are connected to each other between the adjacent pieces of the commutator CM0, and thereby three rotor magnetic poles are formed therebetween. The polarity of these rotor magnetic poles varies depending on the contact state of each piece of the commutator CM0 and the electrode brushes B01 and B02 which changes corresponding to the rotational angle of the rotor. Thereby, a rotational driving force is generated between, for example, a pair of stator magnetic poles of a permanent magnet at the side of a stator (not shown).
With the rotation of the rotor, respective rotor magnetic poles oppose to respective stator magnetic poles in order, and the contact state of each piece of the commutator CM0 and the electrode brushes B01 and B02 changes. Thus, by the variance of the polarity of each rotor magnetic pole in order, the rotor continually rotates.
Specifically, when a voltage is applied to the paired electrode brushes B01 and B02 from the power supply E0, the current flows from one of the electrode brushes B01 and B02 to another through the rotor coils. The magnetic field is generated by the rotor coils, and thereby the rotor magnetic poles are formed. By the action of the magnetic field generated by the rotor coils and the magnetic field generated by the stator magnetic poles, the rotor rotates.
As a method of detecting the rotation of the above-described motor, a rotary encoder method is known. Specifically, in the rotary encoder method, a rotational slit disk having slits on the circumferential surface thereof is provided on a rotation output shaft of the motor or in a power transmission mechanism rotated by the rotation output shaft. The rotation of the motor is detected by the method of detecting the slits on the circumferential surface of the rotational slit disk with a photointerrupter. Although the rotary encoder method allows an accurate detection of the rotation of the motor, space and cost for the rotary encoder constructed by the rotational slit disk, the photointerrupter, and etc. are inevitably increased.
Further, another method of detecting the rotation of the motor from the drive voltage ripple of the motor is described referring to FIGS. 31 and 32. In FIG. 31, a resistor R0 is connected in series to electrode brushes B01 and B02 in a power supplying line for supplying the motor drive current to the electrode brushes B01 and B02 from a drive power supply E0, and the voltage between both terminals of the resistor R0 is detected. In such a way, the ripple waveform of 60xc2x0-period of the drive current as illustrated in FIG. 32 is obtained.
Because the ripple waveform corresponds to the rotational angle position of the rotor, the pulse signal corresponding to the rotational angle position can be obtained by suitably rectifying (shaping) the ripple waveform. Although this another rotation detecting method is advantageous in cost and space, detection errors due to noise, etc. may be caused, so that this another rotation detecting method may be disadvantageous in detection accuracy.
For example, Japanese Laid-open Patent Publication No. 4-127864 describes a method for detecting the rotational speed of a DC motor wherein a rotation detecting brush is provided in addition to a pair of electrode brushes. Similarly, as in the paired electrode brushes, the rotation detecting brush is brought into sliding contact with a commutator so as to extract a voltage applied to the commutator. The rotational speed of the DC motor is detected based on the signal generated by the rotation detecting brush.
Specifically, Japanese Laid-open Patent Publication No. 4-127864 describes a DC motor control circuit illustrated in FIG. 33. Referring to FIG. 33, a rotation detecting brush BD0 is provided to a motor M0 in addition to a pair of electrode brushes B01 and B02. The rotation detecting brush BD0 is connected to a differentiating circuit 101, a time constant reset circuit 102, and a time constant circuit 103 in order. In a comparator 105, the voltage of the output signal from the time constant circuit 103 is applied to a non-inversion input terminal (i.e., +side) of the comparator 105, and the voltage of the output signal from a reference voltage generating device 104 is applied to an inversion input terminal (i.e., xe2x88x92side) of the comparator 105. The output signal from the comparator 105 is connected to one terminal of exciting coils of a relay 107 through a diode 106. Another terminal of the exciting coils of the relay 107 is connected to one terminal of a drive power supply E0. The pair of electrode brushes B01 and B02 is connected to the drive power supply E0 via a contact 107a of the relay 107.
The one terminal of the exciting coils of the relay 107 is connected to a collector of a transistor 109a of a motor starting circuit 109 via a diode 108. The motor starting signal is applied to a base of the transistor 109a via a resistor 109b. A resistor 109c is connected between the base and an emitter of the transistor 109a. The emitter of the transistor 109a is connected to another terminal of the drive power supply E0.
FIG. 34 is a diagram illustrating waveforms of a motor starting signal input to the motor starting circuit 109, a rotation detecting signal SA0 of the rotation detecting brush BD0, an output signal SB0 from the differentiating circuit 101, an output signal SC0 from the time constant circuit 103, an output signal SD0 from the comparator 105, an operation (on/off) signal of the relay 107, and a supply signal applied to a motor M0 from a drive power supply E0.
Next, the operation of the DC motor control circuit of FIG. 33 is described. When the transistor 109a of the motor starting circuit 109 is turned on by the motor starting signal, the relay 107 is turned on and the contact 107a is closed. Thereby, the electric power is supplied to the motor M0 through the electrode brushes B01 and B02, and the motor M0 starts rotating.
With the rotation of the motor M0, pulse train SA0 is output from the rotation detecting brush BD0 and is differentiated in the differentiating circuit 101. Then, signal SB0 which synchronized in the leading edge of each pulse is applied to the time constant reset circuit 102. The time constant reset circuit 102 is synchronized in the signal SB0, and resets the time constant circuit 103. Then, signal SC0 is output from the time constant circuit 103 as illustrated in FIG. 34.
In the normal state in which the motor M0 rotates at a usual rotational speed, the voltage of the output signal SC0 from the time constant circuit 103 does not exceed the reference voltage applied from the reference voltage generating device 104. In this state, output signal SD0 from the comparator 105 is in an xe2x80x9cLxe2x80x9d (low) level, and the relay 107 is excited and keeps ON condition. Thereby, the supply of electricity to the motor M0 is maintained.
However, when the rotational speed of the motor M0 lowers by overloads, etc., the voltage of the output signal SC0 from the time constant circuit 103 exceeds the reference voltage. Thereby, the output signal SD0 from the comparator 105 becomes a xe2x80x9cHxe2x80x9d (high) level, and the exciting current does not flow through the relay 107. Thereby, the relay 107 is turned off, and the contact 107a is opened. As a result, the supply of electricity to the motor M0 is stopped.
Thus, in the above-described DC motor control circuit, the lowering of the rotational speed of the motor M0 is detected, and the excessive current is prevented from keeping flowing in the motor M0 by stopping the DC motor M0.
However, Japanese Laid-open Patent Publication No. 4-127864 describes the DC motor control circuit wherein only when the rotational speed of the motor M0 is lower than a certain rotational speed, the relay 107 is turned off. It does not describe a DC motor control circuit that can detect and control the rotational speed, the rotational position, the cumulative rotation number, and the rotational direction of the DC motor with high accuracy.
Accordingly, an object of the present invention is to provide a novel rotation detecting apparatus and a novel rotation control apparatus that can detect and control at least one of the rotational speed, the rotational direction, the rotational position, and the cumulative rotation number of a DC motor with accuracy. The pulsed output signal from at least one motor rotor rotation detector brush is processed by signal processing circuitry to regulate at least one of the rotational direction, the rotational speed, the cumulative rotation number, and the rotational position of the rotor.